Adenosine compounds for the treatment of diseases caused by parasitic protozoa

ABSTRACT

The compounds 5&#39;-deoxy-5&#39;-(hydroxyethylthio)adenosine (HETA); 5&#39;-deoxy-5&#39;-(monofluorethylthio)adenosine (MFETA); 5&#39;-deoxy-5&#39;-(chloroethylthio)adenosine (CETA); 5&#39;-deoxy-5&#39;-(bromoethylthtio)adenosine (BETA); 5-deoxy-5-(monofluoroethylthio)ribose (MFETR); 5-deoxy-5-(chloroethylthio)ribose (CETR); 5-deoxy-5-(bromoethylthio)ribose (BETR) and 5-deoxy-5-(hydroxyethylthio)ribose (HETR), are described as well as their uses in treating infections caused by 5&#39;-deoxy-5&#39;-methylthioadenosine (MTA) phosphorylase-containing pathogenic microorganisms; in treating infections caused by 5-deoxy-5-methylthioribose (MTR) kinase-containing pathogenic microorganism; and for treating neoplastic diseases.

orylase containing microorganism. Based on the respective abilities of 5-deoxy-5-(monofluoroethylthio)ribose (MFETR) and 5-deoxy-5-(hydroxyethylthio)ribose (HETR) to be converted, respectively to the identical, potentially toxic products, MFETR-1-P and HETR-1-P, in MTR kinase-containing organisms, the compounds HETR and MFETR would be the preferred effective agents for treating infections caused by MTR kinase-containing microorganisms.

The thioribose compounds of the invention, HETR, MFETR, CETR and BETR, may have utility as biocides against microorganisms which contain MTR kinase and which therefore have the ability to phosphorylate the thioribose.

Alternatively, the respective phosphates of the thioriboses may likewise be effective as biocides against microorganisms which lack MTR kinase and which therefore do not have the ability to phosphorylate the thioribose.

Pathogenic microorganisms known to contain MTR kinase include:

Giardia lamblia

Candida albicans

Staphyloccus aureus

Throughout this specification and claims, all temperatures are given in degrees Celsius and weights are given in grams, unless specified otherwise.

I. Preparation of the Compounds

The compound HETA can be produced in accordance with Kikugawa et al. in "Platelet Aggregation Inhibitors. 2. Inhibition of Platelet Aggregation by 5'-,2-,6-, and 8-Substituted Adenosines. J. Med. Chem. 15, 387, 1972. Certain improvements were made which improved the yield from about 50 percent to about 70 percent. Following is a description of the preferred method for producing HETA.

EXAMPLE A Preparation of 5'-deoxy-5'-(hydroxyethylthio)adenosine (HETA)

Mercaptoethanol (8.83 ml) was added to a solution of NaOH (5.19 g) in water (27 ml). After stirring 0.5 hr, this mixture was added to a flask containing 5'-deoxy-5'-chloroadenosine (10 g) and the reaction mixture heated to 80 C on a hot plate with stirring for 2 hours. The flask was removed from the hot plate and allowed to stand at room temperature overnight or longer (3 days). A solidified precipitate remained in the flask, and water was added to facilitate its dissolution into a filterable precipitate. The product was filtered and washed with water. It was then recrystallized from water and the resulting, purified product, filtered and dried. Methanol was added to form a slurry which was then evaporated under vacuum to give 9.4 g HETA (81.8%); mp 190°-192° C. (softens at 120° C.). Elemental analysis was correct for HETA.

When the general procedure of Kikugawa et al. was used, the reaction mixture was heated for one hour. Under these conditions, workup yielded a product which also contained unreacted starting material and which was then retreated with mercaptoethanol solution. Kikugawa's procedure was thus modified so that the reaction mixture was heated for two hours, thereby insuring completeness of reaction. The Kikugawa et al. procedure was modified by omitting the acidification step with acetic acid.

EXAMPLE B Preparation of 5'-Deoxy-5'-(chloroethylthio)adenosine (CETA)

Thionyl chloride (3.7 ml, 4.3 g, 36.2 mM) was added to 31 ml hexamethylphosphoramide (HMPA) at 0° with stirring, under nitrogen. After 30 minutes, HETA (4.0 g, 12.2 mM) in solid form, was introduced slowly to prevent clumping and stirring was continued an additional 2-4 hr at 0° C. until thin layer chromatography (TLC) (CH₂ Cl_(2/) MeOH; 21:4) indicated disappearance of starting material. The contents of the reaction flask were then poured onto an ice-water mixture (200 ml), to form a gummy residue, the pH was adjusted to 9 with ammonium hydroxide and the aqueous mixture was extracted 3 times with 200 ml portions of CH₂ Cl₂. The combined organic extracts were dried over MgSO₄, filtered and evaporated to give an oil (1.9 g), which upon purification by silica gel column chromatography yielded 450 mg (11%) of CETA as a white solid. Elemental analysis was correct for the compound (C₁₂ H₁₆ N₅ O₃ ClS).

EXAMPLE C Preparation of 5'-Deoxy-5'-(bromoethylthio)adenosine (BETA)

Thionyl bromide (1.4 ml, 3.8 g, 18.3 mM) was added to 9.5 ml HMPA cooled at 0.C under argon. The solution was allowed to come to room temperature over 30 minutes and HETA (4.0 g, 12.2 mM) was added in portions as a dry solid. TLC (CH₂ Cl₂ /MeOH; 21:4) showed the reaction to be complete by the end of 3 hr at which time a 400 ml mixture of ice and water was added. The reaction mixture was stirred until complete dissolution was achieved, and the pH was adjusted within the range of 9-10 at 0° C. The cold aqueous mixture was extracted 3 times with 150 ml portions of ethyl acetate. The combined organic extracts were dried over MgSO₄, filtered and evaporated in vacuo to give a semisolid residue. Co-evaporation with CH₂ Cl₂ gave a white solid residue which was purified on a silica gel column. 200 mg (4.2%) of BETA was obtained as a white solid. Elemental analysis was correct for the compound (C₁₂ H₁₀ N₅ O₃ SBr).

EXAMPLE D Preparation of 5'-Deoxy-5'-(monofluoroethylthio)adenosine (MFETA)

(1) A solution of mercaptoethanol (21.7 ml, 24.2 g, 309 mM) and sodium hydroxide (12.65 g, 316 mM) in 72 ml water was stirred with cooling for 30 minutes. The solution was then transferred to a 500 ml beaker and 5'-deoxy-5'-chloro-2',3'-isopropylideneadenosine (42 g, 129 mM) was added with stirring. The resultant mixture was slowly heated to 105°-108° C. and its volume increased to approximately 200 ml by addition of water. Heating and stirring were continued an additional 1.5-2 hours at which time TLC (silica gel, CH₂ Cl₂ /MeOH:22/3) indicated disappearance of starting material and volume was decreased by one half. The reaction mixture was cooled in an ice bath, the aqueous layer decanted, and the highly viscous organic layer dissolved in approximately 200 ml CH₂ Cl₂. This was washed with 3×75 ml H₂ O, dried over MgSO₄ and filtered. The filtrate was stored below 0° C. for several days, allowing the product to crystallize. Recrystallization from CH₂ Cl₂ /MeOH/petroleum ether yielded a first crop of 18.4 g and upon further cooling of the mother liquor, a second crop of 4.9 g. Total recovered yield of 5'-deoxy-5'-(hydroxyethylthio)-2',3'-isopropylideneadenosine was 22.5 g (47.5%) mp 136°-137° C. Elemental analysis was correct for the compound (C₁₅ H₂₁ N₅ O₄ S).

(2) A dried 500 ml round bottom flask containing product from (1) (I0.0 g 27.2 mM) and a magnetic stirring bar, was charged with argon and capped with a rubber septum. Dry CH₂ Cl₂ (250 ml) was injected and the flask then cooled with stirring in a dry ice/ethanol bath for 20 minutes. To this was slowly injected diethylaminosulfur trifluoride (DAST) (10.8 ml, 13.2 g, 81.7 mM). After 40 minutes the flask was transferred to an ice/water bath and after 11/2-2 hours, when TLC (CH₂ Cl₂ /MeOH: 22:3) indicated disappearance of starting material, the reaction mixture was poured into 350 ml of ice cold saturated aqueous sodium bicarbonate. After extraction with 3×300 ml CH₂ Cl₂, the combined organic layers were dried over MgSO₄, filtered and evaporated in vacuo to give a 2.2 g of a residual foam. This was applied to a Florisil column in CH₂ Cl₂ and chromatographed with 500 ml CH₂ Cl₂ and then CH₂ Cl₂ containing 1% MeOH. In this manner, 1.28 g (12.7%) of 5'-deoxy-5'-(monofluoroethylthio)-2',3'-isopropylideneadenosine was obtained as a white solid. Recrystallization from EtOAc/Et₂ O/hexane, gave an analytically pure sample of product (2): mp 113°-114° C. Elemental analysis was correct for the compound (C₁₅ H₂₀ N₅ O₃ SF).

(3) 5'Deoxy-5'-(monofluoroethylthio)-2',3'-isopropylideneadenosine (2.4 g, 3.5 mM) was dissolved in 43 ml 70% formic acid and stirred overnight at room temperature. Solvent was then removed in vacuo to give an oily residue which was repeatedly coevaporated with water and then methanol, to remove traces of formic acid. The residue was then dissolved in a minimum amount of methanol and purified on a silica column to give the compound MFETA (1.26 g, 59%) as a white solid. Elemental analysis was correct for the compound (C₁₃ H₁₈ N₅ O₃ SF.2/3 CH₃ OH).

EXAMPLE E Preparation of 5-Deoxy-5-(hydroxyethylthio)ribose (HETR)

1. Methyl 5-deoxy-5-chloro-2,3-O-isopropylidene-ribofuranoside (MCIR) was prepared from methyl 2,3-isopropylidene ribfuranoside according to Hanessian et al. (Carbohydrate Res. 24, 45, 1972).

2. A solution of NaOH (40 g), mercaptoethanol (11.34 ml) and water (37.5 ml) was stirred at 0° C. for 0.5 hr and then added to a round bottom flask containing MCIR (15.0 g). The reaction mixture was heated with stirring at 80° C. for 3 days and then cooled. The reaction mixture was extracted with ether (3×100 ml) and the combined ether extracts washed with saturated aqueous NaCl. The ether extract was decolorized with Norit, filtered, dried with MgSO₄, filtered and concentrated under vacuum. The residue was chromatographed on a silica gel column to give methyl 5-deoxy-5-hydroxyethylthio-2,3-isopropylidene-ribofuranoside (MHETIR) (10 g).

3. MHETIR (2.0 g) was refluxed in 25 ml 0.1 N sulfuric acid for 1.5 hr, cooled to room temperature, neutralized to pH 8 with 1.0 N NaOH, and then evaporated to dryness under vacuum. The residue obtained in this manner was chromatographed on silica gel to give 941 mg of the desired product, HETR as a syrup.

EXAMPLE F Preparation of 5-Deoxy-5-(monofluoroethylthio)ribose (MFETR)

1. MHETIR (2.0 g) was dissolved in 50 ml dry methylene chloride and cooled to -74° C. Diethylaminosulfur trifluoride (DAST) (3.0 ml) was injected under argon and after 2.5 hr, the reaction mixture was cautiously treated with saturated sodium bicarbonate solution. This was extracted with methylene chloride, the organic extract washed with saturated aqueous NaCl, dried over MgSO₄, filtered and evaporated under vacuum to give 1.89 g crude product. This was chromatographed on silica gel to give 677 mg methyl 5-deoxy-5-monofluoroethylthio-2,3-O-isopropylidene-riboside (MMFETIR).

2. MMFETIR (215 mg) in 0.1 N sulfuric acid (2875 μl) and dioxane (1400 μl) was heated at 80° C. for 2.75 hr. The solution was cooled to room temperature, neutralized with solid barium hydroxide, filtered and evaporated to dryness under vacuum. The 167 mg residue was chromatographed on Florisil to give 19 mg of the desired product, MFETR.

II Testing of the Compounds

EXAMPLE 1A--In Vitro Antitrypanosomal Activity of HETA and other Nucleosides.

The antitrypanosomal effects of HETA and other nucleosides were examined in the Lab 110 EATRO strain of T. b. brucei in culture.

Cells were cultured as described in Bacchi et al. Exp. Parasitol. 68, 392, 1989. Cells were then grown in the presence of the compounds for 3-5 days. Drugs were filtered, sterilized and added aseptically. Control cells achieved a maximum density of 1.5-3.5×10⁷ /ml. Hemocytometer counts were made daily and the results were expressed as a percent of control growth. IC₅₀ plots were obtained by graphing log (drug) vs. percent growth inhibition.

As seen in Table 1A, which also shows the structures of the compounds tested, MFETA, CETA, BETA and HETA all exhibit significant activity in sharp contrast to closely related compounds ETA, PTA, MFPTA and HPTA. Also included in Table 1a are ETR and HETR, the ribose analogs of ETA and HETA. Both compounds were far less effective than HETA, indicating that trypanosomes do not utilize thioribose derivatives via MTA hydrolase and MTR kinase. Included in Table 1 are the IC₅₀ values for pentamidine and berenil, two agents which are in wide clinical use for the treatment of African trypanosomiasis. The activity of HETA is comparable to that of these currently used drugs.

                  TABLE 1     ______________________________________     Trypanocidal Activity of MTA and MTR Analogs against     T. b. brucei procyclic trypanosomes in T.sub.2 medium.      ##STR1##     COMPOUND       R            IC.sub.50 (μM)     ______________________________________     ETA            CH.sub.3 CH.sub.2                                 138     MFETA          FCH.sub.2 CH.sub.2                                 5     CETA           ClCH.sub.2 CH.sub.2                                 2.5     BETA           BrCH.sub.2 CH.sub.2                                 0.5     HETA           HOCH.sub.2 CH.sub.2                                 0.5     PTA            CH.sub.3 CH.sub.2 CH.sub.2                                 46     MFPTA          FCH.sub.2 CH.sub.2 CH.sub.2                                 120     HPTA           HOCH.sub.2 CH.sub.2 CH.sub.2                                 170     ETR*                        >100     HETR*                       >100     BERENIL*                    0.2     PENTAMIDINE*                0.2     ______________________________________      *Structure not shown.

EXAMPLE 1B--Activity of HETA against bloodstream forms of African trypanosomes grown in vitro.

HETA was also evaluated against other bloodstream forms of African trypanosomes grown in vitro.

Cultures were initiated directly from infected mouse blood into Falcon 24 well plates containing 1 ml of Iscoves modified Dulbecco's medium plus 20% horse serum, 2 mM pyruvate, 2 mM glutamine, and 0.2 uM mercaptoethanol. Initial cell counts were 2.5-5.0×10⁵ /ml. Plates were incubated at 37 C in 5 percent CO₂. HETA was dissolved in the medium and filter sterilized. One half the volume of each well was replaced with fresh medium each day.

Cell counts were made daily. Data are given as percent inhibition of growth as determined by hemocytometer counts on day 4 as compared to control cultures without drug.

In Table 2, EATRO 110 is a strain of T. b. brucei; and KETRI 2002, and KETRI 243 are T. b. rhodesiense clinical isolates.

As seen in Table 2, HETA was found to have significant activity against the KETRI 2002 strain, a clinical isolate of T. b. rhodesiense.

                  TABLE 2     ______________________________________     um HETA  EATRO 100    KETRI 2002 KETRI 243     ______________________________________     0.1       0            0         0     0.5      44            0         0     1.0      59           15         0     2.25     70           60         0     ______________________________________

EXAMPLE 2--In Vivo Antitrypanosomal Activity of HETA

The in vivo activity of HETA was demonstrated using the LAB 110 EATRO mouse infection model.

As seen in Table 3, HETA not only gave high cure rates in these infected mice, but did so over a wide dose range, an indication of its minimal toxicity to the host.

                  TABLE 3     ______________________________________     Susceptibility of T. b. brucei LAB 110     EATRO to HETA in vivo.            Dose     Time            Number Cured     Treatment.sup.a              (mg/kg/day)                         (Days)  MSD.sup.b                                       Total % Cured     ______________________________________     None     --         --      4.8.sup.c                                        0/20  0     Molecusol ®              .sup.d     7       4.9   0/5    0     MTA      25         7       5.0   0/5    0              50         7       5.0   0/5    0              100        7       5.0   0/5    0     HETA     25         7       15.3  11/15 73              50         7       14.5  17/25 68              100        7       26.0  13/15 87              150        7       14.5  18/20 90              50         14      18.1   9/15 60     MFETA    10         7       5.0   0/5    0              25         7       11.6  2/5   40              50         7       10.6  0/5    0              100        7       12.0  2/5   40     ______________________________________      .sup.a Animals were treated with surgically implanted miniosmotic pumps      loaded as per manufacturers instructions with MTA, HETA or MFETA suspende      in 10% Molecusol.      .sup.b Mean survival in days of animals dying of infection; this does not      include cured animals.       .sup.c Range of survival of controls was 4-6 days.      .sup.d Pumps were loaded with 10% Molecusol only.

EXAMPLE 3--In Vitro Activity of HETA and other compounds against Isolates of Trichomonas Vaginalis.

Preliminary in vitro evaluation of HETA and other compounds against isolates of Trichomonas vaginalis was done. As seen in Table 4, HETA displays activity against the C1-NIH strain, and CETA was active against a metronidazole(Flagyl)-resistant strain, CDC-85.

Values are expressed as μg of compound per ml of medium required to inhibit growth and motility of the parasite in a multiwell plate assay as described by Meingassner, Mieth, Czok, Lindmark and Muller (1978) Antimicrob. Agents and Chemother. 13, 1-3. The present drug used for treatment metronidazole (Flagyl®) is included for comparison. Strain ATCC 50143 (CDC-85) was refractory to chemotherapeutic dose levels of metronidazole. (ND=not done).

                  TABLE 4     ______________________________________     Minimum lethal concentration (MLC) of compounds against     Trichomonas vaginalis isolates.     ATCC 3001          ATCC 50143     Drug    24 h      48 hr    24 h     48 h     ______________________________________     ETA     >187.5    187.5    >187.5   >187.5     HETA    46.9      11.7     >187.5   ND     MFETA   93.7      23.4     ND       ND     CETA    93.7      23.4     187.5    11.7     Flagyl  6.25      0.78     >800     ND     ______________________________________

EXAMPLE 4--In Vitro Antimalarial Activity of HETA.

In studies undertaken against P. Falciparum, HETA was unexpectedly found to possess activity with an IC₅₀ value of approximately 22 μM. these data support the conclusion HETA has activity against a wide range of microorganisms.

The foregoing data indicate clearly that HETA has activity against a variety of parasitic protozoa. As noted, this agent inhibits an aspect of the metabolism of polyamines, i.e. the metabolism of MTA, whose potential for therapeutic intervention in parasitic organisms has been recognized but not previously exploited. Ghoda et al. [Molecular Biochem. Parasitol 27, 109 (1988] have previously demonstrated the presence in African trypanosomes of an MTA phosphorylase, as distinct from an MTA hydrolase. The apparent basis for the selectivity of HETA in the microorganism as opposed to mammalian cells, relates to a significant difference in the rate at which HETA is metabolized by mammalian and trypanosomal forms of the enzyme MTA phosphorylase. Whereas HETA has been found to be ineffectively metabolized by mammalian MTA phosphorylase, (HETA has a substrate activity of 34% relative to the MTA). HETA is metabolized by the T. b. brucei MTA phosphorylase as effectively as MTA itself as shown in Tables 5 and 6.

                  TABLE 5     ______________________________________     Compounds as Substrates and/or Inhibitors of Mouse     Liver MTA Phosphorylase                MTA Phosphorylase Activity.sup.a                  K.sub.1   Substrate     Compound     (μM)   (% Control)     ______________________________________     MTA          1.3 (K.sub.m)                            100     ETA          1.9       95     MFETA        3.1       64     CETA         12        35     BETA         6.5       38     HETA         26        34     PTA          1.7       102     MFPTA        4.0       66     ______________________________________      .sup.a MTA phosphorylase activity was assayed as described in Sufrin et      al., J. Med. Chem., 32, 997 (1989).

                  TABLE 6     ______________________________________     Activity of compounds as substrates for T. b. brucei MTA     phosphorylase                 Percent Control Activity.sup.a     Substrate     +50 mM PO.sub.4                              No PO.sub.4     ______________________________________     MTA           100        100     ETA           76.2       100     BETA          88.8       120     MFETA         75.3       109.1     CETA          60         94.4     HETA          85         100     PTA           57.5       96.4     MFPTA         47.5       116.4     HPTA          72.5       101.8     ______________________________________      .sup.a MTA phosphorylase was assayed according to Ghoda et al., using 200      μM MTA (saturating) or analogs as substrates. Specific activities of      the dialyzed enzyme preparations were with 50 mM PO.sub.4, 104.97 n      moles/mg protein/h; without PO.sub.4, 28.27 n moles/mg protein/h. Results      are expressed as percent activity compared to as substrate with and      without PO.sub.4, respectively.

Example 5--Therapeutic Evaluation of Compounds

L1210, L5178Y and MOLT-4 cells lines were grown in RPMI 1640 and 10% Nu Serum (Collaborative Research Inc., Lexington, MA) and CCRF-CEM cells were grown in 10% Horse Serum (Gibco Laboratories, Grand Island, NY) and maintained as previously described for suspension cultures by Pera et al. in Cancer Res. 46, 1148, 1986. Cell cultures (0.3×10⁵ cells/ml) were treated with each compound at 0.1 to 1000 μM to determine the concentration that inhibited growth by 50% (IC₅₀) at 48 hr for the L1210 and L5178Y cells and at 96 hr for the CCRF-CEM and MOLT-4 cells. The incubation times allowed approximately 4 cell doublings in each cell line. All compounds were freshly prepared prior to treatment by dissolving in DMSO and diluting in serum-free media. Cells were counted by electron particle counting (Model XF' Coulter Counter; Coulter Electronics, Hialeah, FL.). The data and results are shown in Table 7.

For each compound, the concentrations required to inhibit cell growth by 50% (IC₅₀ values) are shown in Table 7 for two murine leukemic cell lines, L1210 and L5178Y [MTA phosphorylase-deficient and MTA phosphorylase-containing, respectively]and two human leukemic cell lines, CCRF-CEM and MOLT-4 [MTA phosphorylase-deficient and MTA phosphorylase-containing, respectively]. ETA, MFETA, HETA and PTA had lower IC₅₀ values in the L5178Y cells than in the L1210 cells. MFETA was the most potent analog and demonstrated the most significant difference in IC₅₀ values between the two lines. This differential is consistent with the possibility that, in L5178Y cells, MFETA is cleaved by MTA phosphorylase to the growth inhibitory metabolite, 5-monofluoroethylthioribose-1-phosphate (MFETR-1-P).

The compounds of the invention were more potently growth inhibitory in the human CCRF-CEM and MOLT-4 cells and displayed a consistent differential between these cell lines in their IC₅₀ values. MFETA was the most growth inhibitory compound in all four cell lines tested.

                  TABLE 7     ______________________________________     Effects of MTA, ETA, PTA and 5'-Haloalkyl Compounds     on Growth of Paired (MTA Phosphorylase-containing     and MTA Phosphorylase-deficient) Human and Murine     Tumor Cell Lines     Mouse                Human     Cell Line             L1210     L5178Y     CCRF-CEM MOLT-4     Enzyme.sup.1             <20       2253       <20      2230     Activity     Analog  IC.sub.50 (μM)     48 h                 96 h     ______________________________________     MTA     850 ± 120                       200 ± 45                                  150 ± 60                                           11 ± 7     ETA     800 ± 100                       250 ± 100                                   200 ± 100                                           20 ± 10     MFETA   150 ± 50                       60 ± 35  75 ± 20                                           10 ± 3     CETA    250       200        240 ± 90                                           30 ± 20     BETA    150       150        250 ± 50                                           25 ± 10     HETA    1000      500        100      40     PTA     1000      500        160      45     MFPTA   600       600        160      25     ______________________________________      .sup.1 Intracellular MTA phosphorylase activity expressed in pmol/min/mg      protein.

Example 6--In Vivo Therapeutic Evaluation of MFETA

The antitumor effects of MFETA were evaluated in DBA/2N mice (Charles River) who received i.p. transplants of 10⁶ L1210 leukemic cells or 10⁶ L5178Y leukemic cells on day 0 according to protocols described previously by Bernacki et al., Cancer Res. 47, 799, 1987. The increase in life span (% ILS) of treated animals relative to untreated, tumor-bearing animals was used as the measure of their therapeutic effectiveness at specified dose regimens. The data and results are shown in Table 8.

The results of the in vivo studies agree with cell culture data.

                                      TABLE 8     __________________________________________________________________________     Comparative Antitumor Effects of MFETA in L1210     Leukemic Mice and L5178Y Leukemic Mice                        Survival Parameters          Number of                   Dosage.sup.a                        Mean Death                               Range                                   Median                                       Mean ± SD     Tumor          Treated Animals                   (mg/kg)                        Weight (g)                               (days)                                   (days)                                       (days) % ILS.sup.b                                                   P     __________________________________________________________________________     L1201          13       untreated                        22.0   6-8 7   7.1 ± 0.2                                              0    --          5         10  23.7   6-8 8   7.2 ± 0.5                                              14   0.37          5         50  24.5   7-8 8   7.8 ± 0.2                                              14   0.18          10       100  22.8   7-9 8   7.9 ± 0.2                                              14   0.08          5        200  18.4   6-11                                   9   8.8 ± 0.8                                              28   0.01          5        300  18.8   2-3 2   2.2 ± 0.2                                              -72  NS     L5178Y          13       untreated                        21.7   7-10                                   8   8.5 ± 0.2                                              0    --          5         10  19.7   8-10                                   9   9.0 ± 3                                              12   0.22          5         50  21.6   8-11                                   11  10.0 ± 6                                              37   0.03          10       100  23.1   8-12                                   11  10.5 ± 4                                              37   <0.01          5        200  20.4   9-14                                   13  12.4 ± 9                                              62   <0.01          5        300  18.4   2-4 2   2.6 ± 4                                              -75  NS     __________________________________________________________________________      .sup.a MFETA was administered i.p. on days 1, 2, 3, 4, 5 following i.p.      implantation of 10.sup.6 tumor cells on day 0.      .sup.b % ILS is the percentage of increase in life span. 

What is claimed is:
 1. A compound selected from the group consisting of 5'-deoxy-5'-(monofluoroethylthio)adenosine (MFETA); 5'-deoxy-5'-(chloroethylthio)adenosine (CETA) and 5'-deoxy-5,-(bromoethylthio)adenosine (BETA).
 2. The compound 5'-deoxy-5'-(monofluoroethylthio)adenosine (MFETA).
 3. The compound 5'-deoxy-5'-(chloroethylthio)adenosine (CETA).
 4. The compound 5'-deoxy-5'-(bromoethylthio)adenosine (BETA).
 5. A method for treating infections caused by 5'-deoxy-5'-methylthioadenosine (MTA) phosphorylase-containing pathogenic microorganisms which comprises administering a nontoxic, effective amount of an adenosine compound to a human being or an animal in need of such a treatment, wherein said adenosine compound is selected from one or more of the following compounds:' -deoxy-5'-(hydroxyethylthio)adenosine (HETA); 5'-deoxy-5'-(monofluoroethylthio)adenosine (MFETA); 5'-deoxy-5'-(chloroethylthio)adenosine (CETA); and 5'-deoxy-5'-(bromoethylthio)adenosine (BETA).
 6. A method for treating infections caused by 5'-deoxy-5'-methylthioadenosine (MTA) phosphorylase-containing pathogenic microorganisms which comprises administering a nontoxic, effective amount of 5'-deoxy-5'-(hydroxyethylthio)adenosine to a human being or an animal in need of such a treatment.
 7. The method of claim 5 wherein the microorganism is selected from:Trypanosoma brucei brucei. Trypanosoma brucei rhodesiense. Trypanosoma brucei gambiense, Trypanosoma cruzi. Trichomonas vaginalis. Plasmodium falciparum, Leishmania donovani, Leishmania tropica, and Leishmania brasiliensis.
 8. A method for treating infections caused by Trypanosoma brucei brucei, Trypanosoma brucei rhodesiense or Trypanosoma brucei gambiense, which comprises administering a nontoxic, effective amount of an adenosine compound to a human being or an animal in need of such a treatment, wherein said adenosine compound is selected from one or more of the following compounds:' -deoxy-5'-(hydroxyethylthio)adenosine (HETA); 5'-deoxy-5'-(monofluoroethylthio)adenosine (MFETA); 5'-deoxy-5'-(chloroethylthio)adenosine (CETA); and 5'-deoxy-5'-(bromoethylthio)adenosine (BETA).
 9. A method for treating infections caused by Trypanosoma brucei brucei, Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense, which comprises administering a nontoxic, effective amount of 5'-deoxy-5'-(hydroxyethylthio)adenosine to a human being or an animal in need of such a treatment. 